1. Technical Field
The present invention relates to a color conversion technology of color-converting colors of input image data into colors used by a display unit for image display.
2. Related Art
An image display device capable of displaying images using four or more colors has been known (hereinafter, basic colors representing image data are also referred to as “primary colors”). In the image display device, input image data is in three primary colors, and the image data is color-converted in multiple primary colors (e.g., four primary colors). For example, JP-A-2003-295812 discloses a technology for improving brightness of output videos by adding W (white) to R (red), G (green), and B (blue). In the technology, the scaling factor is obtained using values of RGB, and the RGB data is scaled and separated into RGBW data. Further, all colors are converted using the primary colors of the display as primary colors after color conversion without change. Furthermore, JP-A-2000-38950 discloses a technology of dividing a color reproduction range in a display device using multiple primary colors into plural pyramid regions and calculating primary colors RGBC in the respective regions.
However, according to the method disclosed in JP-A-2003-295812, the area of a color filter is smaller in the case of using four primary colors of RGBW than in the case of using the three primary colors, and the colorfulness may be lower. Further, the saturation is lower because of white added after conversion, and the entire saturation in the output video tends to be lower.
Further, according to the method disclosed in JP-A-2000-338950, when the multi-primary color display can encompass only a little of the standard color space in RGB, a color outside of the color reproduction range may not be appropriately reproduced on the display. Specifically, a method of color-range compression of a color outside of the color reproduction range is disclosed in the document. However, the color overlapping may not be appropriately reduced because of mapping on the surface, and further, the color outside of the color reproduction range may not be appropriately reproduced because the result of mapping is greatly affected by the surface and the goal.